Age-related macular degeneration (AMD) is responsible for approx. 9% of the world's blindness, affecting 2 million people in the United States. Pathological neovasculation is one of the main causes of degeneration of the central vision region of the retina. VEGF and its receptors, VEGFR and co-receptor Neuropilin (Nrp) together with plexins, direct this formation of blood vessels, but the receptors also regulate cell survival and proliferation. Over the last decade, anti-VEGF therapy has become a principal mode of treatment for AMD. Several antibodies against VEGF-A, Ranibizumab and off-label use of Bevacizumab, are effective in slowing visual loss in 90% of patients. However, their long term effects on angiogenesis are not yet known and resistance against VEGFR blockade-like treatments has already become a problem. Thus a deeper understanding of Neuropilin/VEGFR/Plexin signaling is needed at the molecular level for the design of more specific agents. Furthermore, both drugs need to be injected directly into the eye every month, making the development of therapeutics that can be administered at least intravenously, if not orally, highly desirable. The proposed project focuses on Neuropilin signaling at the molecular and mechanistic level. As yet there is no detailed structural information for the transmembrane (TM) segment, for the well conserved 46 residues just outside the cell, or for the 44 residue intracellular region of Nrp1. We hypothesize that the relationship between the TM and membrane proximal regions constitutes key parts of the mechanism for transmembrane signaling; specifically the regions are likely to participate in regulatory events in a hierarchica manner. Peptides corresponding to the Nrp1 TM region can inhibit receptor function and angiogenesis. However, insights are needed at the molecular level in order to understand this mechanism and to optimize the peptide inhibitors, utilizing the context of the membrane surrounding regions, for anti- angiogenesis therapy. Our structural studies will synergize with functional studies of Nrp1 that are ongoing in several laboratories. The R21 project has two exploratory aims: Aim 1 will take steps towards the determination of the neuropilin- 1 (Nrp1) transmembrane (TM) dimer structure by solution NMR spectroscopy and characterization of TM inhibitory peptide interactions, also the context of the intracellular and a portion of the extracellular region. Aim 2 examines the intracellular 44 residue region and its newly discovered interaction with the Nrp1 co- receptor plexin-D1.